Inhibition Mechanism And Alleviating Technology Of Full Continuous Reflux Of Digestate For Straw Biogas

In large scale biogas projects of straw,reflux of digestate can reduce the amount of dilution water and dispose digestate effectively and conveniently.It is one of the most promising technology of digestate reduction.But now the technology of full continuous reflux of digestate had not yet matured.In practical engineering application,eventually lead to instability of digestion and lower the biogas production rate,even lead to system crash in severe condition.So,the method of lower reflux ratio to ensure stable operation of biogas projects is more applicated in practice.However,the dilution water need to be supplement in this condition,and cannot solve the problem that disposal of digestate by reduce the amount of digestate radically.Based on this,this paper focused on technology improvement and process optimization of full continuous reflux of digestate.For the purpose of providing scientific basics for improving effect of full continuous reflux of digestate and digestate reduction,the effects of full continuous reflux of digestate on the characteristics of rice straw digestion,influencing mechanism of reflux of digestate on gas production and relevant countermeasures was investigated.The effects of long-time reflux of digestate on gas production was investigated by CSTR and batch test with rice straw.And then,the factor of inhibiting gas production was make preliminary analysis,and the technology method that mitigating inhibition of gas production was investigated.The main results are as follows.(1)Effects of full continuous reflux of digestate on the characteristics of rice straw anaerobic digestion.The results showed gas production inhibited obviously in this condition.The specific biogas yields and volumetric biogas production rate declined to 186 mL·g-1 TS,226 mL·g-1 VS and 0.56 L·L-1·d-1,respectively,in the inhibiting period(from 81th day to 105th day),which decreased by around 24%compared with those in the stable period(from 41th day to 60 day).The ammonia concentration dropped from 640 mg·L-1 to 185 mg·L-1 with the decrease rate of 71%.The VS content rose from 0.36%to 2.00%which the increase rate of 4.55 times.The total concentration of main metal ions(K+、Ca2+、Mg2+)rose to 4.13 g·L-1 with the increase rate of 342%,thereinto,K+ concentration is about 83.25%.(2)Influencing mechanism of full continuous reflux of digestate on gas production for rice straw anaerobic digestion.The results showed that gas production inhibited when nitrogen concentration is insufficient,and the TS biogas yields,VS biogas yields and volumetric biogas production rate recovered to 93%,87%and 92%compared with those in the stable period,respectively,if supplemented nitrogen nutrition.But nitrogen concentration excessed optimal range which from 200 mg·L-1 to 800 mg·L-1 if supplemented nitrogen continuously.The gas production of rice straw anaerobic digestion inhibited obviously when cation(K+、Ca2+、Mg2+)concentration accumulated to 6 g·L-1,however,it is no obvious impacts on gas production when cation(K+、Ca2+、Mg2+)concentration below 4 g·L-1.(3)Research of alleviating technology of gas production under the condition that full continuous reflux of digestate.The results showed that inhibiting effects of salt can be alleviated by anaerobic co-digestion of rice straw and pig manure.In batch experiment,under the condition that cation concentration was 6 g·L-1,and TS methane yields for co-digestion increased 31.90%and 48.28%compared with pure rice straw anaerobic digestion,respectively.In continuous experiment,TS biogas yields,VS biogas yields and volumetric biogas production rate for treatment group increased 34.1%～39.5%,46.4%-51.6%and 34.6%～39.5%compared with control group,respectively.Anaerobic co-digestion of rice straw and pig manure helped dissolved salt transform to sediment.In addition,it helped reduce concentration of K+ by forming sediment or eliminate K+ with biogas residue,and then,it helped alleviating disoperation to anaerobe and inhibition to gas production.In conclusion,the concentration of ammonia nitrogen dropped under the condition that full continuous reflux of digestate,and the gas production recovered partly by supplementing nitrogen nutrient real time.It is helpful to alleviate disoperation to anaerobe by adding pig manure to reduce concentration of K~+.